Epoxy molding composition and method of molding with same



EPOXY MOLDING COMPOSITION AND METHOD OF MOLDING WITH SAME Luther L.Bolstad, t.,Louis Park, Minn., assignor to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn, a corporation of Delaware NoDrawing. Application March 18, 1955 Serial No. 495,341

20 Claims. (Cl. 26037) This invention relates to resin-containingmolding compositions including epoxy ether condensation polymers havingthe following structure yl)-2,2-propane, bis-(4-hydroxy-2-tertiary butylphenyl)- 2,2-propane, bis-(Z-dihydroxy-naphthyl)-methane,1,5-dihydroxynaphthalene, and the like]. Such epoxy ethers are describedin the patents to Bradley No. 2,500,600 and to Newey No. 2,553,718, andreference is made to these patents for descriptions of these resins andmethods of preparing the same. Epoxy ether resins made by condensingepichlorhydrin and bis-(4-hydroxyphenyl)-2,2- propane (bis-phenol) areavailable commercially.

The present invention is an improvement over the copending applicationof Jerome L. Formo et al., Serial No. 306,306, filed August 25, 1952,entitled Resin Composition and assigned to the same assignee as thepresent invention.

An important object of the present invention is to provide a rapidlycuring molding composition curable by heat, including an epoxy etherresin which composition will not set up or cure over relatively longperiods of time at room temperature (in other words, will be char:acterized by a long shelf life); which will not adhere, when set orcured, to the surface of the mold (whether made of metal or othermaterial) within which the mold: ing operation is carried out; andwhich, when set or cured, will be characterized by extremely highelectrical insulation resistance, high impact resistance and lowmoisture absorption.

A specific object of this invention is to provide a molding compositionof the nature indicated which when cured or set is characterized bydistinct heat conductive properties.

Another specific object of the invention is to provide a moldingcomposition of the nature indicated modified so as to render the set orcured material electrically contares atenr du'ctive, the electricalconductivity being uniform throughout the cured or set material.

A further object of the present invention is to provide a heat curableepoxy resin molding composition which is characterizedby having anunusually rapid curing cycle,

in the range of a minute or less.

I Other and further objects and features of the present invention willbecome apparent from the following description and appendedclaims.

The improved molding compositions of this invention comprise an epoxyresin of the type described, a diamino curing agent and a phenol-typeaccelerator. The mixture may include, for example, up to 30 parts of adiamine,

curing agent. per parts of resin and up to about 10 parts of acceleratorper 100 parts of resin-diamine compound. The epoxy resins employed inthe invention are characterized by having the number designated in theabove-noted structural formula as n falling within the range of frommore than 0 up to about 20. It should be noted, in this connection, thatthe epoxide resins in question are mixtures of compounds each having thein'- dicated structure, and that the number herein designated as n isthe average of the integral numbers n whichcharacterize each compoundmaking up these mixtures.

If desired, the epoxy resin content of the molding composition may bedistributed between several epoxy resinshaving n" numbers of differentvalues, as long as the average of these numbers falls within the abovedisclosed range, due allowance being made for the proportion of theseveral epoxy resins.

The epoxy resin content of the molding compositions "n Percent Amine 025;l=5' 2.5. :2; 12 6. 25:1:2' 1. 5&1"

At values of n falling between the tabulated-values the amount of amineis adjusted proportionally.

The accelerator is selected from the class consisting of phenol,catechol, resorcinol, and cresol. These acf celerators when added to thecomposition catalyze the reaction between the epoxy resin and thep,p'-diamino-' diphenylmethane, causing the reaction to proceed at'a'much faster rate as evidenced by the shorter reaction times and curingcycles required. I prefer to add the acclerator in an amount rangingfrom greater than 0% up to about 10% based on the weight of the resinand the p,p'-diamino-diphenylmethane hardner, with the pre-;

ferred range being substantially between 4 and 8%. Table I shows the geltimes for various epoxy 'resin diaminodiphenylmethane acceleratormixtures. The resin mixture includes 4 parts resin to 1 part diamino:

' diphenylmethane. The epoxy resin employed is a liquid resin having avalue for "12 equal to about 1.

ssets? TABLE I Grams Accelerator Per 10 Gel Time Accelerator GrarrsResinin minutes dlaminophenylat 300 F.

methane Mixture 2 Phenol 0. 4 2. 25 0.6 1. 5 0.8 1.15 1.0 0.7 0 4. 658'? it Cetechol 6 D. 7 0. 8 O. 45 1. 0 0. 35 0 g '2 Rcsorctnol 0. 4 1. 90.6 1.05 0.8 0. 95 0 4. 6 8': 2 12 Cruel 0.6 1.15 0.8 1.7 1. 0 1. 5 1.5 1. 25

It is believed that when the above disclosed mixtures of epoxide resinsand diaminodiphenylmethane are heatcured, there takes place a crosslinkage through reaction of the active hydrogens of the amines with theepoxide groups. The accelerators appear to catalyze the reaction betweenthe resin and the diaminodiphenylmethane, however, since no freeaccelerator is available after curing has been accomplished, it isbelieved that the accelerator is chemically combined into the cured orfinal product. The physical properties of the resin cured withaccelerator appear to be somewhat improved over those of the resin curedwithout accelerator provided the accelerator is not included in theresin mixture in amounts exceeding about (See Table II.) The shelf lifeof these accelerator-containing resins is somewhat shorter than that ofsimilar resins without the accelerator added; however, even with theaccelerator, the shelf life is generally in the range of a few monthswhich is sufiiciently long to permit normal molding operations andprocedures to be followed. The resulting compounds are of novel chemicalstructure, which explains the unusual properties of the heat-curedmaterials prepared according to the present invention.

In Table II below there are tabulated the various physical propertiesfor a composition prepared with the accelerator addition and without theaddition. The data indicates the superior characteristics obtained whenthe accelerator is included in the composition; In each case, thecomposition was prepared as follows:

The molding compositions of the present invention further includeconventional fillers or pigments such as glass fibers or granules,asbestos, silica, perlite, biotite or mica, titanium dioxide, chromeyellow, zinc oxide, walnut'shell, wood flour, carbon black, acetyleneblack or resinous material such as nylon fiber. As disclosedhereinbelow, the incorporation of acetylene black or like electricallyconducting materials and of titanium dioxide or like heat conductingmaterials leads to the formation of resinous materials having uniqueproperties.

The amount of fillers or pigments included with our molding compositionsmay be varied from or less up to as much as 95% depending upon theproperties desired in the heat-cured material and upon the specificfillers and/ or pigments employed. The particle size distribution of thefillers is often the factor determining the amount to be used for aparticular purpose. Good results have beenobtained by using variousfillers in the percentages (by weight of the molding composition)tabulated as follows:

It should be understood that the molding compositions may' comprise amixture of several fillers and/ or pigments.

The moisture content of the molding compositions should be less than 1%(by weight) and preferably less than 0.5%

In connection with the preparation of our molding composition, it shouldbe noted that epoxy resins having n at least equal to 2 are solids. Butresins having "12 equal to 1 are liquids. When only solid epoxy resinsare included, all the ingredients may be mixed in dry form, as bymilling on a two roller mill. However, when fibrous fillers'areincluded, I prefer to dissolve the resin in a suitable solvent (such asacetone) and to impregnate the fibrous filler with this solution beforethe ingredients of the molding composition are milled or otherwisemixed. It is, of course, always possible, even when only solidingredients are present in the final molding mixture, to dissolve theresin or resins in solvents and to mix the resulting solutions with theremaining (dry) ingredients. Best results are obtained by simply mixingall the ingredients on a two roller mill, the accelerator being addedlast, the resin being dissolved in a solvent when ever fibrous fillersare employed. When relatively large amounts of resin are employed alongwith relatively small quantities of accelerator, the accelerator ispreferably added dispersed in a solvent such as acetone in order topermit a more homogeneous mixture to be obtained. If it is undesirableto use a solvent in mixing the fibrous fillers with the resin, thesefillers may be added gradually to the other ingredients.

Whenever solvents are used in making up these molding compositions,provision is made for removing such solvents, as by milling until thesolvents have evaporated or by drying the solvent-containing moldingcomposition subsequent to its preparation, or by using molds havingsuitable breathing apertures.

The resulting molding compositions are characterized by relatively longshelf life. Samples containing accelerator have been kept for severalmonths and longer periods without becoming unworkable. (Samples of thesame composition, however, in the absence of the accelerator have ashelf life of a year or more.) For all practical purposes, my moldingcompositions may be considered as meeting any and all normal storagerequirements that may possibly be encountered.

In spite of their relatively long shelf lives, my molding compositionsset or cure rapidly when molded at an ele vated temperature. The curetime ranges from several seconds (when the molding composition ispreheated) to about 5 minutes (when particularly slow setting epoxyresins are molded without any preheating). Theaverage cure time rangesfrom less than a minute to about 2 minutes. The curing temperatureranges from 250 to 380 F. and usually falls within the range of from 280to 350 F. The preferred range is from 300 to 315 F. The molding pressureranges from 10 to 15 up to about 2000 pounds per square inch, dependingon the contents and nature of the filler (if any) of the moldingcomposition, preheating (if any) of the molding composition, moldingtemperature, and other factors. Generally, enough pressure is used toform the molding composition into a'so lid or dense product. At atemperature of from 250 to 350.". F., the molding pressure willordinarily range upwardly from 100 pounds per square inch. Whenextremely rapid curing cycles are used, such as in the range of 30seconds or less, it may be desirable to postcure the molded article bybaking at about 200 F. to 300 F. for a period ranging from less than anhour up to about a day. This post-cure baking will generally enhance thephysical properties of the molded article by increasing its impactstrength and raising its heat distortion temperature.

Any conventional molds may be used, such as the wellknown compressionand transfer molds usually employed for molding resins.

After molding has been completed, the molded articles are easilyreleased from the molds (whether made of metal or other material). Inother words, there is no trouble due to adhesion of the molded articlesto the mold surfaces. If desired, however, a suitable mold re leasecompound may be utilized either milled integral with the moldingcomposition or coated onto the mold surfaces. I have found that ingeneral, fatty-acid esters are satisfactory in this regard.

The molded articles prepared as disclosed hereinabove are characterizedby highly desirable properties. Thus, moisture absorption is less than4% and can be reduced to 0.1% or less through the addition of lowmoisture absorbing fillers. The electrical insulation resistance can bemade to exceed megohm-cm. The impact strength exceeds 0.5 ft. lb./in. ofnotch (Izod) and can be made to exceed 5.0 by the addition of fibrousfillers. When titanium dioxide (in an amount of more than 50% by weightof the molding composition) is used as a filler, the molded articles arecharacterized by a remarkable heat conductivity coupled with highelectrical insulation resistance and high impact strength. Whenacetylene black (in amounts ranging from 2 to 40% or more by weight ofthe molding composition) or other electrically conducting materials areused as fillers, the molded products are electrically conducting, andthis conductance is uniform throughout the articles. Particularly goodresults are obtained in the range of from 8 to 10%. Such uniformconductivity has heretofore never been obtained in molded resinousarticles.

Specific examples of molding compositions according to the presentinvention are given hereinbelow. In these specific examples, epoxyresins prepared from epichlorhydrin and bis-phenol were used. Epoxyresin No. 1 had equal to 2.0. Epoxy resin No. 2 had an n equal to about0. The diamino-diphenylmethane is indicated in the following table as D.A. D. P. M.;

molding temperature was from 300 to 315 F.; molding pressure, from 150to 300 pounds per square inch; and molding time, from 3 to 5 minutes:

Example I A base molding composition having the following constituentswas milled together:

Before removing from the mill, 9 parts of catechol were added to thiscomposition and homogeneously mixed therewith. After milling, thismaterial was cured at a temperature of 300 F. and was found to set up infrom 2 to 5 minutes. The physical and electrical properties weresomewhat superior to those of a similar compound without the catecholaccelerator addition.

Example II To the base molding compound of Example I, 22.5 parts byweight of catechol were added. This material was molded at 300 F. andsetup or cured in less than 1' minute and had excellent physical andelectrical properties.

Example Ill To the base molding composition of Example I, 45.0 parts byweight of catechol were added. This material set up rapidly, beingwholely cured in substantially less than 1 minute at 300 F. Theproperties did not appear to be adversely affected.

Example IV To the base molding composition of Example I, 22.5 parts byweight of resorcinol were added and milled into the composition. Thismaterial was molded at 300 F. and was found to cure in less than 1minute.

Of course, various fillers such as previously listed herein may beutilized in compositions as listed herein.

In Table II below there is given the comparative values of variousphysical properties obtained from typical samples of molding compoundsincluding and not including the accelerator of the present invention.Sample #1 was prepared with the base molding compound of Example Iincluding the catechol addition. Sample #2 was prepared from the samebase molding compound, however, there was no accelerator added to themixture. Each sample was post baked at 200 F. for a period of 8 hours.

Similar results to those disclosed in the above specific examples areobtained when proceeding in exactly the same manner except forsubstituting, in place of resin No. 1, epoxy resins made with bis-phenoland having n equal, respectively, to 6 and to 12. The same applies toother epoxy resins made with other dihydric phenols.

Many details of composition and procedure may be varied withoutdeparting from the principles of this invention. It is, therefore, notmy purpose to limit the patent granted on this application otherwisethan necessitated by the scope of the appended claims.

I claim:

1. A composition of matter comprising para, para diamino diphenylmethanetogether with an epoxy resin having the structural formula wherein Rstands for the hydrocarbon radical of a dihydric phenol and n stands fora number ranging from more than 0 up to about 20, and an acceleratortaken from the classconsisting of phenol, catechol, resorcinol, andcresol, the said diamino compound being commingled with said epoxy resinin an amount ranging from /& to 30% by weight of said resin, the saidaccelerator being. included in said composition in an amount rangingfrom greater than 0% to about 10% based on the weight of said resin anddiamino compound.

2. A composition of matter comprising para, para assume C CHa" wherein Rstands for the hydrocarbon. radicalof'a dihydric phenol and n stands fora number ranging from more than 0 up to about 20, and-an acceleratorcomprising catechol, the said diamino compound included in said'composition. in' an amount rangingifrom I i to 30% byfweightiof saidresin, thesaid accelerator being. included in said'composition' in'anamount ranging from greater than 0% to about 10%, based on the weight ofsaid resin and diamin'o cbnipoundf- 3'; A composition a'ccording'f toclaim 1 in which the amount of said diarr'iinocompoundis correlated withthe magnitude of the said number represented by n in saidformulaaccordingfto the following table Percent Diamlno Compound theamount of said diamino compound being proportionally adjusted for othervalues of n.

4: A composition according to claiml in which R stands for thehydrocarbon radical of bis-(4-hydroxyand subjecting thelsaidcompositionto heat in the range of from about 250" F. to about 380 F. and pressurein the range of from about 10p. s. i.- to about'2000 p. s. i.

8. A composition-accordingto claim 3 inwhich R 4 stands for thehydrocarbon radical of bis-(4-hydroxy- 9.-A composltlon according toclaim 3- comprising titanium dioxide as a filler;

10. A composition accordingto claim 3 comprising acetyl'eneblack as afiller.

11. A pressure'ranges from 10 to 2000 pounds per square inch, saidpressure being applied for from 5 seconds to 3 minutes, said pressurebeing applied 'at atemperature of from 250 to 380 F.

12. As a novel chemical composition, the cured composition in accordancewith claim 1.

13.'A composition according to claim 4 comprising titanium dioxide as afiller.

14. A composition according to claim 4 comprising acetylene black as afiller.

15. A composition according to claim 4 comprising a filler in an amountof from 20m 95%" of the total weight of said composition.

16. A composition accordingto claim 1 comprising two epoxyresins whereinthe said n numbers have dissimilarvalues:

17. A method of making a molded resinous articlecharacterizedbyheat-conductivity which comprises providingaicompositionaccordingto claim 5 and subjecting the saidcompo'sition'to'heat andpressure.

18. A method of making a molded resinous article characterized byuniform electrical conductivity which comprises providing a compositionaccording to claim 6 and subjecting saidcomposition to heat andpressure.

19. A cured resinous articlehaving a compositionvin accordance withclaim 51 20. A' cured resinous article havinga composition inaccordancewith claim 6.

References Cited in the file of this patent UNITED STATES PATENTS2,512,997 Bixler June 27, 1950 2,615,007 Greenlee Oct. 21, 1952 2,773,048 Forrno et al. Dec. 4, 1956 FOREIGN PATENTS 680,997 Great BritainOct. 15, 1952 method according to claim 7 in which said

1. A COMPOSITION OF MATTER COMPRISING PARA, PARA'' DIAMINODIPHENYLMETHANE TOGETHER WITH AN EPOXY RESIN HAVING THE STRUCTURALFORMULA